1. Field of the Invention
The present invention is related generally to a detector objective for use in scanning microscopes.
2. Description of the Related Art
The electrical properties of modern, integrated micro-electronic and opto-electronic components are critically influenced by the geometrical dimensions of their sub-structures. It is therefore particularly important to observe close dimensional tolerances as an indispensable prerequisite to the manufacture of functional components with constant physical-electrical properties, particularly when the geometrical dimensions of the structures being generated by modern lithography methods are in the micrometer and sub-micrometer range.
There is, therefore, an increasing need for high resolution imaging systems that enable process proximate inspection and exact measurement of the structures generated in all phases of development and manufacturing of integrated micro electronic and opto-electronic components. Scanning electron microscopes have proven especially suitable for these purposes. Micrometer and sub-micrometer structures are capable of being visually evaluated through the use of scanning electron microsocopes, and errors and deviations from the desired patterns are capable of being identified. Topographical data such as lengths, widths, heights or angles of inclination of the structures are capable of being acquired and interpreted with scanning electron microscopes. It must thereby be assured during all examinations of electrical components using scanning electron microscopes that modifications of the substrate, such as occur, for example, due to contamination and radiation damage, are avoided.
Conventional scanning electron microscopes achieve a resolution of a few nanometers only at high accelerating voltages of above approximately 20 kv. Resist structures as well as the circuits are damaged due to such high energy electrons, and non-conductive and/or poorly conductive surface regions of the specimen under examination are electrically charged. It is a standard practice in scanning electron microscopy to metalize the specimen to supress these charges. However, such metalization deteriorates the resolution and the image quality so that it is not suitable for examination of such small microelectronic and opto-electronic components. Furthermore, their function is destroyed or modified in an inadmissible way by the application of a metal layer.